This invention relates to medical devices and more particularly to syringes with a device for locking the plunger in place with respect to the barrel of the syringe of the type disclosed in applicants' assignee's copending application by Ewalt et al., Ser. No. 06/743,127 filed on June 10, 1985 entitled "Syringe Locking Device".
There are several devices known for restraining a syringe plunger in an extended position while a vacuum is held in the syringe barrel in front of the plunger piston. Such devices might include stepped stops on the plunger such as are shown in U.S. Pat. Nos. 3,882,849 and 3,938,505. These devices, however, require that the standard plunger and/or syringe barrel be modified in some way to provide the locking mechanism. Other devices, such as that shown in U.S. Pat. No. 4,386,606, require a separate moving part to accomplish the desired function. Such moving parts may be relatively difficult to manufacture and to use, and may be less reliable than a device without such an additional moving part.
All these devices would seem to necessitate fairly major changes in the syringe manufacturing process and would possibly add significantly to the cost of a syringe.